Segment Reporting Schedule of Revenues from External Customers and Long-Lived Assets (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net	$ 278,622	$ 276,135	$ 267,562	$ 262,903	$ 276,279	$ 273,163	$ 263,139	$ 260,927	$ 1,085,222	$ 1,073,508	$ 981,080
Property, Plant and Equipment, Net	149,014				138,824				149,014	138,824	125,418
Income Before Interest Expense and Taxes	90,450	89,120	84,134	82,827	87,917	84,596	81,869	79,037	346,531	333,419	297,280
Other Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									464,335	478,414	431,136
Property, Plant and Equipment, Net	49,209				47,759				49,209	47,759	42,063
UNITED STATES
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									515,643	487,252	454,617
Property, Plant and Equipment, Net	83,748				73,870				83,748	73,870	66,092
CANADA
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									105,244	107,842	95,327
Property, Plant and Equipment, Net	$ 16,057				$ 17,195				$ 16,057	$ 17,195	$ 17,263